Method and equipment for moulding an article produced from paperboard

ABSTRACT

A method and equipment for moulding an article produced from paperboard or cardboard. Moulding is carried out by a moulding tool that mechanically works the board; and to improve its mouldability, momentary irradiation on the microwave frequency is exerted on the board. The method applies to the manufacture of packages and disposable containers made of paperboard or cardboard; for example, to the forming of a rolled-up or folded rim around a drinking cup, mug or a container, the forming of a stiffening crease or projection on a paperboard container, or to press moulding of paperboard containers or plates.

The invention relates to a method for mechanically moulding an articlethat is produced from paperboard or cardboard. The invention alsorelates to equipment for applying the method.

Containers, disposable tableware and packages are made of paperboard bymeans of a technique comprising the following typical stages ofoperation: cutting a blank from a board web, folding and/or bending andjoint sealing the blank to give the item being made its final shape.Paperboard containers and plates are also produced by press-moulding ordeep-drawing the blank. Other moulding machining operations ofpaperboard products include providing paperboard containers, such ascups and mugs, with a rolled-up or creased rim or a so-called mouthroll, and forming annular reinforcing ribs or similar creases on thesides of the paperboard vessels or packages.

In the press moulding of paperboard articles, the blank is broughtbetween a pair of heated press moulds, whereby the paperboard bends orfolds under compression, forming creases on the rim or in the corners ofthe article thus formed. Heating is necessary to make the deformation ofthe paperboard permanent. Press moulding has been used in themanufacture of foodstuff dishes and plates made of paperboard inparticular.

The purpose of the mouth roll that is formed on paperboard drinking cupsand mugs, on the one hand, is to stiffen the cup and, on the other hand,to provide the desired touch with the user's mouth, when enjoying abeverage. The mouth roll is provided by a tool that bends and/or pressesthe paperboard, mostly at the final stage of manufacture of a cup thatis already bent and sealed. To make the mouth roll sufficiently tightand permanent, a heated tool is used, as well as additives, such asoils, and moistening of the paperboard. However, as fluctuations in themoisture of air have an effect on it, the moistening of the paperboardin particular is difficult to control in practice; in addition,moistened paperboard tends to warp or, when becoming too damp,completely loses its stiffness.

The purpose of the invention is to provide a new solution for themechanical moulding of paperboard articles, such as containers,tableware, packages and similar products, avoiding the problems of priorart mentioned above. The method according to the invention ischaracterized in that a spot of the board is moulded mechanically bymeans of a moulding tool while irradiation of microwave-frequency isSimultaneously exerted on said spot.

The basic idea of the invention is to provide a local effect ofradiation that heats the spot of the board that is to be moulded andmakes the board deformable for the time the heating is maintained. Asthe board does not require moistening or the use of oil or other similaradditives, and there is no need to heat the actual moulding tools, themoulding is easy to control.

According to the invention, microwave radiation is exerted on themouldable spots of the board, its frequency being in the range of 1 to1000 GHz (corresponding to a wavelength interval of about 0.03-30 cm),preferably in the range of 2 to 100 GHz, the radiation being absorbed bythe board. Paperboard or cardboard intrinsically contains about 5 to 9%of moisture; whereby there are water molecules attached to the freehydroxyl groups in the cellulose fibres, forming bridges between thefibres. The radiation hitting the board instantly vaporizes the water sothat the bonds between fibres are dissolved, while heat is absorbed bythe board. The board thus turns plastic for a moment, and it can beworked mechanically. When the board solidifies into the form it has beengiven by the mechanical, the result of the moulding operation becomespermanent.

In the invention, a radiation frequency of 2.45 GHz can be used(corresponding to a wavelength of 12.2 cm), which is standard inconventional microwave ovens made for cooking. The frequency in questionis somewhat below the absorption peak of water, its purpose being toprevent the heating effect from excessively concentrating on the surfacelayer of the food. However, as the object of irradiation of theinvention is a fairly thin board, the most preferable frequency rangethat maximally utilizes the radiation is slightly higher, closer to theabsorption peak of water.

In the invention, the irradiation pulse is sufficient, if it vaporizesthe moisture contained by the board in the area that is moulded. It ispreferable, if in momentary heating the moisture evaporates inside theboard without exiting the board. In practice, the duration of theirradiation pulse can be about 0.1 to 1.0 seconds, corresponding to thetime it takes to mould a single article in mass production. It ispreferable to start irradiation slightly before starting the mechanicalworking by the tool.

The mechanical moulding of board products according to the invention cancomprise measures that bend, fold or press the board, or combinationsthereof. The essential objects of the invention include localexpansions, protrusions or reinforcements that are provided on boardarticles, such as the rolled-up or creased rims of cups, mugs or plates.Similarly, further objects of the invention include creases orprojections formed to the sides of the board articles, such ascontainers or packages, circling around them for the purpose ofstiffening the article. Other objects of the invention comprise pressmoulding or deep drawing paperboard or cardboard articles, such ascontainers and plates, wherein the moulding provides bent or foldedcreases in the corners of the article or annularly on the rim of thearticle.

The equipment according to the invention for moulding articles ofpaperboard or cardboard in accordance with the description abovecomprises not only the moulding tool that mechanically works the spot ofthe board that is to be moulded, but also a source of radiation thatproduces radiation on the microwave frequency, from which source anirradiation pulse of a short duration can be directed at the mouldablespot of the board. The source of radiation can selectively be installedas part of the moving moulding tool, part of the stationary counterpartof the moving tool or completely separate from the moulding tool and itscounterpart.

In the following, the invention is explained in detail with the aid ofexamples and with reference to the appended drawings, in which:

FIG. 1 shows the moulding of a mouth roll around the mouth of apaperboard drinking cup by means of irradiators and a moulding tool atthe home position of the motion of the tool parts,

FIG. 2 shows the tool according to FIG. 1 coming to the end point of itsmovement, wherein the mouth roll is formed on the mouth of the cup,

FIG. 3 shows a moulding tool that produces an annular, projecting creaseto the side of the drinking cup,

FIG. 4, which is the section IV-IV of FIG. 3, shows the moulding tool inthe home position of its movement,

FIG. 5 shows the moulding tool at the end point of its movement,corresponding to FIG. 4,

FIG. 6 shows a drinking cup made of paperboard with a mouth roll mouldedby means of the moulding tool according to FIGS. 1 and 2,

FIG. 7 shows a drinking cup comprising, in addition to the mouth roll, aprojecting, annular crease moulded thereon by means of the moulding toolaccording to FIGS. 3 to 5,

FIG. 8 shows a frozen food paperboard container, which is moulded bypress moulding combined with irradiation, and

FIG. 9 shows a disposable plate made of paperboard and moulded by acorresponding method.

The tool according to FIGS. 1 and 2 for moulding the mouth roll on apaperboard drinking cup 1 comprises a vertically reciprocating strikingtool 2, a stationary base 3 that supports the cup, and a carrier ring 4that supports the side of the cup and works as the stationarycounterpart for the striking tool. For forming the mouth roll, anannular groove 5 is formed on the lower surface of the striking tool 2.In the home position of the moulding movement according to FIG. 1, thedrinking cup 1, the rolling of the mouth of which is the last stage ofoperation in its manufacturing process, is supported by the base 3 andthe carrier ring 4 so that the rim 6 of the cup rises slightly above thesurface of the carrier ring. While the striking tool 2 carries out itsworking motion that is directed downwards from the position in FIG. 1,the rim 6 of the cup projects into the groove 5, which forces the rim tobend out and down and to roll up to form a projecting expansion aroundthe mouth of the cup, wherein the rim is twisted, for example, by aboutone and a half revolutions before the striking tool 2 hits thecounterpart 4.

In order to make the cup board mouldable and the mouth roll 7 thusformed permanent, an irradiation pulse on the microwave frequency isdirected from the irradiators 8 towards the rim 6 of the cup, the pulsebeing indicated by broken lines 9 in FIG. 1. Irradiation may be startedjust before the tool 2 comes into contact with the cup 1, and will becontinued during the moulding operation, preferably up to the moment thetool 2 hits the counterpart 4. Depending on the humidity of the ambientair, the moisture content of the paperboard is in the range of 5 to 9%.The radiation frequency can be, for example, 2.45 GHz, which is used inconventional microwave ovens, and the pulse duration can be 0.1 seconds,for example. To prevent the radiation from spreading, the irradiators 8are installed inside a protecting casing 10 that surrounds the cup 1. InFIG. 1, there are irradiators 8 arranged on both the inner surface ofthe protective casing 10 and in the carrier ring 4 surrounding the cup,but, in practice, it is sufficient to have irradiators installed in onlyone of them. Installing the irradiators in the moving striking tool 2would also be feasible. The purpose of the irradiation is to heat thecup board at the rim 6 of the cup so that the humidity contained by thepaperboard evaporates for the time the mouth roll 7 is being formed fromthe rim. The evaporation of water and the resulting heating of thepaperboard make the paperboard deformable for a moment, whereby themouth roll formed on the cup remains permanent, because the paperboardcools off and returns to its normal rigidity immediately after theforming.

FIGS. 3 to 5 show a moulding process, wherein an annular crease 11 thatstiffens the cup and projects form the side of the cup is formed on apaperboard drinking cup 1′ (cf FIG. 7). The cup 1′ is placed on the base3 and supported at its side by the carrier ring 4 in a similar fashionas in FIGS. 1 and 2. An annular groove 12 is formed on the surface ofthe carrier ring 4 that supports the cup, its shape corresponding to thecrease that is to be made in the cup. The moving moulding tool 13 islowered inside the cup 1′ so that its lower end is level with the groove12 of the carrier ring. The irradiators 8 are installed on the verticalaxis 14 of the moving tool 13, and an irradiation pulse 9 on themicrowave frequency is exerted on the side of the cup at the point wherethe crease is to be formed. The frequency and the duration of theirradiation can be as those mentioned in connection with FIGS. 1 and 2.

The operation of the moulding tool 13 in forming the crease 11 isillustrated in FIGS. 4 and 5. Curved clamping parts 16 are connected tothe vertical axis 14 of the tool 13 by means of horizontal telescopearms 15, corresponding to the groove 12 of the carrier ring and thecrease 111 that is to be created; the parts being shown in FIG. 4 intheir retracted home positions corresponding to. FIG. 3 and, in FIG. 5,as projecting into the groove of the carrier ring, whereby the side ofthe cup 1′ is pressed between the clamping parts 16 that are arrangedinto a ring and the bottom of the groove 12. The crease 11, which isprovided by the heating produced by the momentary irradiation pulse 9,and which corresponds to the recession, thus remains permanent.

FIGS. 6 and 7 show finished paperboard drinking cups 1, 1′, which areformed according to the invention. The drinking cup 1 according to FIG.6 is provided with a mouth roll 7, which can be made by means of themoulding process described in FIGS. 1 and 2. The drinking cup 1′according to FIG. 7 is provided, in addition to the mouth roll 7, withan annular crease 11, which projects from the side of the cup and whichcan be made by means of the moulding process described in FIGS. 3 to 5.

The mechanical moulding of board products according to the invention,utilizing irradiation on the microwave frequency, can also be applied toproducts made by means of press moulding or deep-drawing. In themanufacture of the products, conventional moulding tools as such can beused, having irradiators installed therein as accessories, and anirradiation pulse on the microwave frequency can be directed from theirradiators to the spots of the board that are to be moulded. FIG. 8shows an example of a frozen food paperboard container 17, which, inthis way, is press-moulded from a blank, its folds 18 and/orcorrugations 19 of the corners being formed by means of irradiation.FIG. 9 shows a disposable paperboard plate 20, which is formed from ablank in a similar manner.

It is obvious to those skilled in the art that the differentapplications of the invention are not limited to the above examples, butcan vary within the following claims.

1. A method for mechanically moulding an article that is produced frompaperboard or cardboard, comprising a spot of the board is mouldedmechanically by moulding tool while irradiation microwave frequency issimultaneously exerted on said spot.
 2. A method according to claim 1,wherein the frequency of the radiation used is 1 to 1000 GHz.
 3. Amethod according to claim 1, wherein the irradiation is sufficient forevaporating the moisture contained by the board at the spot beingmoulded.
 4. A method according to claim 1, wherein an irradiation pulseof a short duration is exerted on the spot of the board that is beingmoulded, said pulse momentarily evaporating humidity contained by theboard without causing a significant exit of moisture from the board. 5.A method according to claim 1, wherein the board is moulded by bending,folding and/or pressing.
 6. A method according to claim 1, theirradiation is started before the spot of the board that is to bemoulded is worked by the moulding tool.
 7. A method according to claim1, wherein the duration of the irradiation pulses is about 0.1 to 1.0seconds.
 8. A method according to claim 1, wherein the method is used toprovide a local protrusion or reinforcement to an article produced frompaperboard.
 9. A method according to claim 8, wherein the methodprovides a rolled-up or folded rim to an article produced frompaperboard, such as a container, a drinking cup, a mug or a plate.
 10. Amethod according to claim 8, wherein the method provides a crease or aprojection to an article produced from paperboard.
 11. A methodaccording to claim 1, wherein said method is used for folding orpressing a paperboard blank into the form of an article.
 12. A methodaccording to claim 11, wherein said method is used in the press mouldingof paperboard containers or plates.
 13. Equipment for moulding anarticle produced from paperboard or cardboard, comprising a mouldingtool that mechanically works the spot of the board being moulded,wherein the equipment further includes a source of microwave frequencyradiation, from which an irradiation pulse of a short duration can beexerted on the spot of the board that is being moulded.
 14. Equipmentaccording to claim 13, wherein the source of radiation is installed aspart of a moving moulding tool.
 15. Equipment according to claim 13,wherein the source of radiation is installed as part of a stationarycounterpart of the moulding tool.
 16. Equipment according to claim 13,wherein the source of radiation is a separate part from the mouldingtool and/or the counterpart.
 17. Equipment according to claim 13,wherein the moulding tool comprises means for producing a rim on themouth of a paperboard article by rolling up or folding of the board. 18.Equipment according to claim 13, wherein the moulding tool is acompression-moulding press that presses a paperboard blank into the formof a container.
 19. Equipment according to claim 13, wherein theequipment is surrounded with a protective casing, which prevents themicrowaves from spreading into the environment.